文摘
Cholapod anion receptors can achieve high affinities while maintaining compatibility with nonpolarmedia. Previously they have been shown to transport anions across cell and vesicle membranes. In thepresent work, the scope of the architecture is expanded and structure-selectivity relationships areinvestigated. Eight new receptors have been synthesized, with up to six H-bond donor centers. Using Cram'sextraction method, these compounds plus five known examples have been tested for binding to sevenmonovalent anions (tetraethylammonium salts, wet chloroform as solvent). Association constants in excessof 1010 M-1 have been measured for several pairings. Selectivities vary with receptor geometry, as expected.More remarkably, they also depend on receptor strength: more powerful receptors show a wider range ofbinding free energies, and therefore a greater spread of Ka(X-)/Ka(Y-). This "affinity-selectivity" effect canbe derived from empirical relationships for H-bond strengths, and could prove widely operative insupramolecular chemistry.